Traditional current sensors employ a shunt. A shunt is typically a low ohmic resistor in the order of 1 mOhm or less; the shunt has a well-defined resistance so that via Ohm's law a current flowing through the shunt can be measured at high accuracy. Typically, a shunt may be made of special alloy composition with zero temperature coefficient of resistivity (TCR). Recently, also plain copper or aluminum shunts are in use—here, a temperature sensor is attached to the shunt which measures the temperature of the shunt and accounts for the nominal TCR.
However, current sensors that employ a dedicated shunt face certain restrictions and drawbacks. For example, current sensors are often used on a substrate or on a printed circuit board (PCB). Typically, in such a scenario a thick copper layer is in the center or core of the laminate or substrate. The current to be measured (e.g., the primary current) flows in the core layer. For current measurements where a dedicated shunt is employed, it is typically required to interrupt the conductor to open the current path in the core layer. Further, the primary current needs to be routed to the surface of the substrate. This makes a design of the system more complex and requires considerable efforts in terms of routing. For example, it may be required to provide a large number of vias. In particular, it may be required that the vias can handle the comparatively large current. Here, it is desirable that the vias do not add a significant resistance to avoid heating of the system and increased power dissipation. The shunt is then soldered or UV-welded to the vias at the top of the substrate.
Further, in a scenario as explained above, typically a predominant part of the primary current needs to flow via solder at interfaces where the primary conductor is interrupted. Typically, a maximum allowable current density is comparably lower in the solder then in the conductor, because the solder is more prone to electromigration. Typically, the solder degrades due to the current flow even when the temperature is moderate. In consequence, it is typically required to employ comparatively large areas for the solder interfaces to avoid wear out. This, in turn, increases the required space of the substrate. Typically, this results in an increase of costs.
Further, relying on shunts can cause comparably high insertion losses and, thus, a large power is typically wasted for the current measurement.
A further disadvantage of employing a dedicated shunt is that a difference in Seebeck-coefficients of the employed materials may give rise to thermo offset. This may be the case if the shunt is made from a particular alloy having a constant TCR while sense contacts that detect a voltage drop over the shunt are made from electrolytic copper. Such a material pairing typically gives rise to thermo offsets when the two sense contacts are at different temperatures. This will cause a zero-point error of the current measurement. Moreover, such errors that are caused by thermo offsets typically exhibit a poorly defined lifetime drift which makes them difficult to compensate for.